The present invention is directed to the manufacture of sheet material containers such as sheet metal drums, casks and the like, typically of cylindrical or polygonal cross section.
It is well known to seam end closures to the open ends of container bodies with a double or triple seam. The resulting seamed container has a chime which protrudes radially outwardly with respect to the sidewall of the container body. In the case of triple-seamed containers the outer diameter of seven layers of sheet metal defining a triple seam is thus somewhat greater than that of conventional double seamed containers.
This relatively small difference in the overall diameter may be critical and produce considerable lost space when loading 55 gallon drums in standard ISO shipping containers, namely by reducing the numbers of drums in row. In some cases the resulting total loss of capacity of the shipping container may be up to 15%.
It has been contemplated to reduce the diameter of the container body prior to the seaming operation in order to reduce the radial projection of the chime of the container. Such a method has been used successfully in the case of small-sized containers where similar problems of reducing lost space exists.
The reduction of the diameter of the ends of a container body involves a separate step prior to seaming, with attendant extra costs. Further, the end closure would have to be correspondingly reduced to adapt to the reduced diameter of the container body ends.